As an inkjet head of an inkjet recording apparatus, those using various discharging systems are known. For example, a piezoelectric inkjet head discharges an ink by electrical oscillation of a piezoelectric element in an ink chamber.
In the piezoelectric system, an electrical charge necessary for discharging an ink is applied to a piezoelectric element, and therefore, an ink containing a highly electrically conductive pigment such as a metal powder typified by a metallic ink is affected by the electrical charge and cannot be discharged normally, or the piezoelectric element itself is broken down due to electrical conduction in the ink in some cases.
On the other hand, a pigment composed of a metal to be blended in a metallic ink or the like is required to have brightness. However, for example, a pigment or the like composed of a metal containing aluminum as a main component easily reacts with water or the like in the air, and therefore has disadvantages that the metallic luster is deteriorated, the color is changed, hydrogen gas is generated, and so on. As those which solve the disadvantages, there is known a surface-coated aluminum pigment which is obtained by coating the surface of aluminum with a coating film containing an alkoxysilane as a main component, and therefore has water resistance and the like while maintaining brightness.